JP2556984B2 - Endoscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an endoscope.

[Prior Art] JP-A-49-1215 shown in FIG. 27 as an endoscope objective lens.
A retrofocus type such as the one described in No. 47 is known. In this endoscope objective lens, a lens system is configured so as to be incident vertically on the incident surface of the image guide 1. Therefore, there are drawbacks such as large distortion and a large outer diameter of the lens as compared with the diameter of the image.

On the other hand, in recent years, in an electronic endoscope that uses a solid-state image sensor instead of an image guide, as in the case of using an image fiber even when the chief ray is obliquely incident on the solid-state image sensor as shown in FIG. The image is transmitted without causing any drawbacks. Therefore, the objective lens is constructed as shown in Japanese Patent Laid-Open No. 61-35414 so that the distortion is small, the total length of the lens system is short, the outer diameter is small, the wide angle is wide, and the peripheral light quantity is sufficiently obtained. Things are known.

In each of the endoscope objective lenses disclosed in JP-A-49-121547 and JP-A-61-35414, the image distance (the distance from the final lens to the image forming point) is short.

In these conventional examples, since the former uses an image guide, the longitudinal direction of the image guide coincides with the longitudinal direction of the scope, and the optical axis of the optical system needs to coincide with them. It is desirable that the image distance be short in order to make the tip portion of the endoscope compact.

Further, in the latter objective lens used in an endoscope using a solid-state image pickup element, it is desirable that the image distance is short for compactness. However, the solid-state image sensor currently used is not practical because the size of the package is much larger than that of the image pickup section and the thickness of the endoscope becomes too thick when incorporated in the endoscope. In the frame transfer type solid-state imaging device (charge-coupled device), the lid stacking part is arranged next to the imaging part, and the size of the solid-state imaging device is twice as large as that of the imaging part. Not suitable for.

In order to solve such a drawback, as in JP-A-60-26981, a retrofocus type objective lens is used, a prism is arranged behind the objective lens and the optical path is bent, and the solid-state image pickup device has an endoscope whose longitudinal direction is an endoscope. It is known that they are arranged so as to be parallel to the central axis of. FIG. 29 is a diagram showing an example thereof, in which a prism behind the retrofocus type objective lens provided in the tip portion of the endoscope is arranged, and the solid-state image pickup element is at the center of the endoscope on the exit side of this prism. The longitudinal direction is arranged on the shaft in parallel with the axial direction. With this configuration, it is possible to prevent the diameter of the distal end portion of the endoscope from increasing due to the solid-state image sensor.

However, since the objective lens is a retrofocus type, it is difficult to reduce the diameter of the lens. Also 30th
As shown in the figure, the principal ray is almost parallel to the optical axis, and the image distance is long because the prism is placed behind the objective lens, and the ray height is higher at the incident position of the prism in front of the solid-state image sensor. Becomes high, and it becomes difficult to make the prism compact and compact. Further, since the longitudinal direction of the solid-state image sensor is along the central axis of the endoscope, the distance from the tip of the endoscope to the rear end of the solid-state image sensor becomes long, which makes it difficult to insert the endoscope into a bent portion. The problem of occurs.

[Problems to be Solved by the Invention] The present invention provides an endoscope including a solid-state imaging device and a tip optical system, a lens system that is fine, and a tip portion that is small and compact including a housing of the solid-state imaging device. It is a thing.

[Means for Solving the Problems] The present invention includes a solid-state image sensor and an objective lens, a prism is arranged in front of the solid-state image sensor, and the longitudinal direction of the solid-state image sensor is obliquely inclined with respect to the axial direction of the endoscope. The objective lens is composed of a front lens group having a negative refracting power in order from the object side, an intermediate lens group having a positive refracting power as a whole, and an air surface. The following conditions (1) and (2) are used in a lens system in which a final lens unit having a negative refractive power including a lens having a concave surface in contact with it and a diaphragm disposed between the most object side surface and the most image side surface of the intermediate group. ) And (3) are satisfied.

_{(1) | θ 1 |>} | θ 2/3 | (2) | f B /f|>1.4 (3) | h 1 / f 1 |> 1.15 · | h 4 / f 4 | However, θ ₁ is The angle between the off-axis chief ray and the optical axis at the maximum angle of view, θ ₂ is the angle between the off-axis chief ray at the maximum angle of view and the off-axis ray passing through the aperture periphery, f _B is the back focus of the optical system, f ₁ is the focal length of the front group, f ₄ is the focal length of the final group, h ₁ is the average ray height at each lens surface of the front group through which the off-axis chief ray passes at the maximum angle of view, h ₄ is the maximum The average value of the ray heights at each lens surface of the final group through which the off-axis chief ray at the angle of view passes, and f is the focal length of the entire system.

In the present invention, the objective lens of the endoscope is such that the principal ray on the exit side is not parallel to the optical axis but is a divergent ray, so to speak, it is a divergent system for the principal ray. It is possible to reduce the luminous flux diameter in the above, and to make the prism small in size, and at the same time, to make the outer diameter of the lens small so that the storage space for the lens system and the solid-state image pickup device can be made small, thereby realizing an endoscope having a small diameter.

Further, in the optical system of the present invention, when the solid-state image sensor is arranged obliquely, the diameter of the endoscope can be made smaller than that when it is arranged parallel to the optical axis, and the distance from the tip to the final surface of the solid-state image sensor is reduced. It can be shortened and can be made into a more compact endoscope.

As described above, and as shown in FIG. 1, when the principal ray is not parallel to the optical axis but is a divergent system, the light beam diameter at the front surface of the prism can be made smaller, and the prism can be made smaller. In order to form a divergent system in this way, the angle formed by the off-axis chief ray at the maximum angle of view and the optical axis is θ ₁ , and the off-axis chief ray at the maximum angle of view and the off-axis ray passing through the periphery of the diaphragm are formed. When the angle is θ ₂ , it is desirable to satisfy the above condition, that is, the following relationship.

_{(1) | θ 1 |>} | θ 2/3 | is not satisfied this condition sufficiently without obtained without a light beam to a small therefore the prism becomes large, no effect of the image sensor diagonally to obtain.

Next, it is necessary to make the image distance sufficiently long as shown in FIGS. That is, it is necessary to place a prism behind the lens system in order to place the image sensor diagonally or parallel to the optical axis, as well as an optical low-pass filter (crystal), an infrared cut filter, and a cover glass for protecting the solid-state image sensor. This is because it needs to be placed.

Solid-state imaging devices are generally sensitive to infrared light as well, and thus an infrared cut filter is required to cut them.

Further, in the case of a colorization system using a mosaic filter array as a solid-state image sensor, an optical low pass filter is required to remove moire.

Further, a cover glass for protecting the image sensor is required to prevent dust from adhering to the image sensor.

For the above reasons, it is necessary to dispose the prism, the infrared cut filter, the optical low pass filter, and the cover glass for protecting the image sensor between the image sensors of the lens system, and therefore the image distance must be sufficiently long.

Since the image distance changes depending on the object distance, this is the bass focus which is the image distance when the object distance is infinite.
When the focal length of the entire system is represented by f when it is defined by f _B, it is necessary to satisfy the following condition (2).

(2) | f _B /f|>1.4 If the condition (2) is not satisfied, the back focus f _B becomes small, that is, the image distance becomes short, and it becomes difficult to arrange the filters and the like. .

Further, the condition (3) is an important condition for aberration correction. That the product of the average value h ₁ and power ₁ of the ray height at the lens surfaces of the foremost group of off-axis principal ray passes at a maximum field angle, the final group of off-axis principal ray passes at a maximum angle of view including a concave surface When comparing the average value h ₄ of the ray heights at the respective lens surfaces and the product of the power, it is important to satisfy the following conditions.

| h ₁ · ₁ |> 1.15 · | h ₄ · ₄ | For example, in an electronic endoscope using a solid-state image sensor 3 as shown in Fig. 28, the chief ray 4 is a fixed image sensor as shown in this figure. Even if the light beam is incident on 3 at an angle, there is no defect as in the case of using the image fiber, and the image is transmitted.

According to the present invention, by disposing the final group including a lens having a concave surface on the object side in front of the image surface, the distortion aberration, which is a drawback of the conventional retrofocus type endoscope objective lens, is large, and This is a solution to the problem of large diameter.

Further, in the objective lens of the present invention, the aperture stop S is arranged between the front surface and the rear surface of the intermediate group, which makes it possible to correct distortion and the like. That is, if the aperture stop is arranged at the above-mentioned location, the incident angle of the chief ray to the image plane can be increased by the amount that the aperture is lowered backward as compared with the usual telecentric type retrofocus endoscope objective lens, It is effective for correcting distortion. In addition, if the diaphragm is placed at the above position, the asymmetry of the lens system when the diaphragm is placed between the retrofocus type divergent group and the converging group (before the diaphragm, only the negative group is positive after the diaphragm) However, it is also advantageous for the correction of coma aberration.

Further, as an optical system similar to the lens system of the present invention, there is an optical system of Japanese Patent Publication No. 42-23896 shown in FIG. In this optical system, the refracting power | h ₄ / f ₄ | of the chief ray due to the final group is too strong, so the greater the angle of view, the greater the incidence of the chief ray on the image plane. The amount of peripheral light is significantly reduced by the law.

In view of this point, in the preferred embodiment of the present invention, the refracting power of the chief ray | h ₁ / f ₁ |
h ₄ / f ₄ | Stronger, which widens the lens angle in the front group, and in the final group moderately bends the chief ray to eliminate distortion in the range where peripheral light intensity does not decrease significantly. To the image surface) to reduce the lens outer diameter. For that purpose, it is necessary to determine the focal length f ₁ of the front group and the focal length f ₄ of the last group so as to satisfy the condition (3). Therefore, if the condition (3) is not satisfied, the distortion cannot be corrected and the lens system becomes large.

As described above, in terms of the lens configuration, a lens group having a negative refractive power (front group), a lens group having a positive refractive power (intermediate group), and a lens group including a strong concave surface (final group) in order from the object side. ), It is necessary to make the diaphragm come between the most object side surface and the most image side surface of the lens unit having a positive refractive power.

In order to have a long back focus as described above and an appropriate divergence system with respect to the chief ray in such a configuration, it is desirable to do the following.

First, it is important to distribute the power between the lens unit having a negative refractive power, which is the frontmost lens unit, and the other lens units. Since the negative refraction travel group is arranged closest to the image side, the back focus is generally short. Therefore, in order to obtain sufficient back focus, it is necessary to give the front group a function of lengthening the back focus.

If the focal length of the front group is f ₁ , the focal length of the entire system is f, and the magnification of the rear group (composite system of the intermediate group and the final group) is β, the following relationship holds.

From the relationship of f = f ₁ × β, and referring to FIG. 4, it is understood that f _B can be increased by increasing β by shortening | f ₁ |. If the value of β is the same, f _B can be increased if the focal length of the rear group (the system behind the front group) is large. However, in this case, the focal length of the rear lens group has an appropriate range and there is an upper limit because it goes against compactness. Also, if the focal length of the rear group becomes small with the same value of β, f _B cannot be extended and there is a lower limit.

From the above, it is desirable that the focal length f _{1 of the} foremost lens group and the focal length f ₂₃₄ of the combined system of the intermediate lens group and the last lens group be set within the ranges of the following conditions (4) and (5).

(4) | f ₁ / f | <1 (5) When 0.4 <| f ₂₃₄ | / f <2 | f ₁ / f |> 1, f _B cannot be obtained sufficiently. As well
Even if | f ₂₃₄ | / f becomes smaller than 0.4, f _B cannot be obtained sufficiently. Furthermore, if | f ₂₃₄ | / f becomes larger than 2, it cannot be made compact.

Further, the present invention has defined the balance of the refractive power of the foremost group and the last group as described above, but it is further desirable to appropriately set the radius of curvature R ₁ of the concave surface of the foremost group and the curvature radius R ₄ of the concave surface of the final group. It is preferable to satisfy the following conditions (6) and (7).

(6) 0.2 <| R ₁ | / f <10 (7) 0.2 <| R ₄ | / f <10 Beyond the lower limits of these conditions, it becomes difficult to correct coma aberration well, and so-called coma aberration flatness is reduced. It will disappear and a bend will occur. If the upper limits of the conditions are exceeded, the lens diameters of the front lens group and the last lens group cannot be made small, and the exit pupil is made to be a diverging system, and the lens diameter of the last lens group and the optical elements such as prisms arranged thereafter can be made small. I can't.

EXAMPLES Next, examples of the endoscope objective lens of the present invention will be described.

Example 1 f = 1, F / 8.7, IH = 0.821 2ω = 78.8 ° r ₁ ＝ ∞ d ₁ ＝ 0.1138 n ₁ = 1.88300 ν ₁ ＝ 40.78 r ₂ ＝ 0.4116 d ₂ ＝ 0.1434 r ₃ ＝ 0.7405 d ₃ ＝ 0.3301 n ₂ = 1.72825 ν ₂ ＝ 28.46 r ₄ ＝ －0.5552 d ₄ ＝ 0.0911 n ₃ ＝ 1.72916 ν ₃ ＝ 54.68 r ₅ ＝ 1.5126 d ₅ ＝ 0.0455 r ₆ ＝ ∞ d ₆ ＝ 0.3415 n ₄ ＝ 1.51633 ν ₄ ＝ 64.15 r ₇ = ∞ _{(stop) d 7 = 0.0455 r 8 =} ∞ d 8 = 0.1707 n 5 = 1.51633 ν 5 = 64.15 r 9 = -0.6941 d 9 = 0.1480 r 10 = 1.4316 d 10 = 0.2504 n 6 = 1.51633 ν 6 = 64.15 r ₁₁ = -0.7847 d ₁₁ = 0.1366 r ₁₂ = -0.6779 d ₁₂ = 0.0911 n ₇ = 1.84666 v ₇ = 23.88 r ₁₃ = -1.4783 d ₁₃ = 0.1480 r ₁₄ = ∞ d ₁₄ = 0.7967 n ₈ = 1.54869 v ₈ ＝ 45.55 r ₁₅ ＝ ∞ d ₁₅ ＝ 1.4466 n ₉ ＝ 1.68893 ν ₉ ＝ 31.08 r ₁₆ ＝ ∞ d ₁₆ ＝ 0.0046 r ₁₇ ＝ ∞ d ₁₇ ＝ 0.5566 n ₁₀ ＝ 1.68893 ν ₁₀ ＝ 31.08 r ₁₈ ＝ ∞ ｜ θ ₁ | − | Θ ₂ /3|=|−17.5°|−|13.28°/3|>0 f _B /f=1.76,|h ₁ / f ₁ | / | h ₄ / f ₄ | = 4.65 | f ₁ | /f=0.466,|f ₂₃₄ | /f=0.843 Example 2 f = 1, F / 12, IH = 0.839 2ω = 79.9 ° r ₁ ＝ ∞ d ₁ ＝ 0.1301 n ₁ ＝ 1.88300 ν ₁ ＝ 40.78 r ₂ ＝ 0.5568 d ₂ ＝ 0.6251 r ₃ ＝ 9.0785 d ₃ ＝ 0.7785 n ₂ = 1.60342 ν ₂ ＝ 38.01 r ₄ ＝ －1.0737 d ₄ ＝ 0.1162 r ₅ ＝ ∞ d ₅ ＝ 0.7460 n ₃ ＝ 1.51633 ν ₃ ＝ 64.15 r ₆ ＝ ∞ (diaphragm) d ₆ ＝ 0.1162 _{r 7 = 1.4999 d 7 = 0.5461} n 4 = 1.51633 ν 4 = 64.15 r 8 = -0.9017 d 8 = 0.2324 r 9 = -0.6921 d 9 = 0.1487 n 5 = 1.84666 ν 5 = 23.78 r 10 = ∞ d 10 = 0.1859 n ₆ = 1.88300 ν ₆ ＝ 40.78 r ₁₁ ＝ －1.7704 d ₁₁ ＝ 0.1162 r ₁₂ ＝ ∞ d ₁₂ ＝ 0.8134 n ₇ ＝ 1.54869 ν ₇ ＝ 45.55 r ₁₃ ＝ ∞ d ₁₃ ＝ 1.7936 n ₈ ＝ 1.68893 ν ₈ ＝ 31.08 r ₁₄ ＝ ∞ d ₁₄ ＝ 0.0005 r ₁₅ ＝ ∞ d ₁₅ ＝ 0.2515 n ₉ ＝ 1.68893 ν ₉ ＝ 31.08 r ₁₆ ＝ ∞ d ₁₆ ＝ 0.0004 r ₁₇ ＝ ∞ d ₁₇ ＝ 0.1162 n ₁₀ ＝ 1.51633 ν ₁₀ ＝ 64.15 r ₁₈ ＝ ∞ ｜ θ ₁ |-| θ ₂ /3|=|-17.0°｜-|2.4°/3|>0 f _B /f=1.74>1.4 | h ₁ / f ₁ | / | h ₄ / f ₄ | = 4.80> 1.15 | f ₁ | /f=0.631 <1, | f ₂₃₄ | /f=1.204 Example 3 f = 1, F / 12, IH = 0.843 2ω = 80.3 ° r ₁ ＝ ∞ d ₁ ＝ 0.1307 n ₁ = 1.88300 ν ₁ ＝ 40.78 r ₂ ＝ 0.5594 d ₂ ＝ 0.2802 r ₃ ＝ ∞ d ₃ ＝ 0.8872 n ₂ ＝ 1.88300 ν ₂ ＝ 40.78 r ₄ ＝ ∞ d ₄ ＝ 0.0934 r ₅ ＝ 10.8137 d ₅ ＝ 0.4179 n ₃ ＝ 1.60342 ν ₃ ＝ 38.01 r _{6 = -1.0834 d 6 = 0.1167 r} 7 = ∞ d 7 = 0.7495 n 4 = 1.51633 ν 4 = 64.15 r 8 = ∞ ( _{stop) d 8 = 0.1167 r 9 =} 1.5069 d 9 = 0.5487 n 5 = 1.51633 ν 5 = _{64.15 r 10 = -0.9059 d 10 =} 0.2335 r 11 = -0.6953 d 11 = 0.1494 n 6 = 1.84666 ν 6 = 23.78 r 12 = ∞ d 12 = 0.1868 n 7 = 1.88300 ν 7 = 40.78 r 13 = -1.7787 d 12 ＝ 0.1167 r ₁₄ ＝ ∞ d ₁₄ ＝ 0.8172 n ₈ ＝ 1.54869 ν ₈ ＝ 45.55 r ₁₅ ＝ ∞ d ₁₅ ＝ 1.8020 n ₉ ＝ 1.68893 ν ₉ ＝ 31.08 r ₁₆ ＝ ∞ d ₁₆ ＝ 0.0005 r ₁₇ ＝ ∞ d ₁₇ ＝ 0.2526 _{n 10 = 1.68893 ν 10 = 31.08} r 18 = ∞ d 18 = 0.0004 r 19 = ∞ d 19 = 0.1167 n 11 = 1.51633 ν 11 = 64.15 r 20 = ∞ | θ 1 | - | ₂ /3|=|-17.0 ° | - | 2.4 ° _{/ 3 |> 0 f B /f=1.75>1.4} | h 1 / f 1 | / | h 4 / f 4 | = 4.78> 1.15 | f 1 | /f=0.634<1,|f ₂₃₄ | /f=1.204 example 4 f = 1, F / 8 , IH = 0.811 2ω = 78.1 ° _{r 1 = ∞ d 1 = 0.1124} n 1 = 1.88300 ν 1 = 40.78 r ₂ = 0.3826 d ₂ = 0.1566 r ₃ = 0.7213 d ₃ = 0.3147 n ₂ = 1.72825 v ₂ = 28.46 r ₄ = -0.5618 d ₄ = 0.0899 n ₃ = 1.72916 v ₃ = 54.68 r ₅ = 1.7290 d ₅ = 0.2885 r ₆ = ∞ _{(stop) d 6 = 0.0225 r 7 =} 1.9806 d 7 = 0.1798 n 4 = 1.51633 ν 4 = 64.15 r 8 = -0.6210 d 8 = 0.0225 r 9 = 1.4344 d 9 = 0.2247 n 5 = 1.51633 ν 5 = 64.15 _{r 10 = -0.8141 d 10 = 0.0718} r 11 = -0.5977 d 11 = 0.1124 n 6 = 1.84666 ν 6 = 23.78 r 12 = -2.1423 d 12 = 0.2247 r 13 = ∞ d 13 = 0.6742 n 7 = 1.51633 ν 7 = _{64.15 r 14 = ∞ d 14 =} 1.9101 n 8 = 1.68893 ν 8 = 31.08 r 15 = ∞ d 15 = 0.1348 n 9 = 1.51633 ν 9 = 64.15 r 16 = ∞ | θ 1 | - | θ 2/3 | = | -20.0 ° | - | 3.6 ° _{/ 3 |> 0 f B /} f _{1.73> 1.4 | h 1 / f} 1 | / | h 4 / f 4 | = 4.81> 1.15 | f 1 | /f=0.433 <1, | f 234 | /f=0.741 Example 5 f = 1, F / 8.0, IH = 0.714 2ω = 71.1 ° r ₁ ＝ ∞ d ₁ ＝ 0.0990 n ₁ = 1.88300 ν ₁ ＝ 40.78 r ₂ ＝ 0.3364 d ₂ ＝ 0.1384 r ₃ ＝ 0.7525 d ₃ ＝ 0.2178 n ₂ = 1.72825 ν ₂ ＝ 28.46 r _{4 = -0.5937 d 4 = 0.0792 n} 3 = 1.72916 ν 2 = 54.68 r 5 = -6.6363 d 5 = 0.2001 r 6 = ∞ ( _{stop) d 6 = 0.0198 r 7 =} 8.9097 d 7 = 0.1584 n 4 = 1.51633 ν 4 _{= 64.15 r 8 = -0.5278 d 8} = 0.0198 r 9 = 1.4245 d 9 = 0.1979 n 9 = 1.51633 ν 5 = 64.15 r 10 = -0.7237 d 10 = 0.0771 r 11 = -0.5271 d 11 = 0.0990 n 6 = 1.84666 ν _{6 = 23.78 r 12 = -2.0374 d} 12 = 0.0792 r 13 = ∞ d 13 = 0.5937 n 7 = 1.51633 ν 7 = 64.15 r 14 = ∞ d 14 = 1.6822 n 8 = 1.68893 ν 8 = 31.08 r 15 = ∞ d 15 ＝ 0.2969 n ₉ ＝ 1.51633 ν ₉ ＝ 64.15 r ₁₆ ＝ ∞ ｜ θ ₁ | − ｜ θ ₂ /3|=｜-20°｜−|3.6°/3|＞0 f _B /f=1.48>1.4 | h ₁ / f ₁ | / | h ₄ / f ₄ | ＝ 3.54 ＞ 1.15 | f ₁ | /f=0.381 <1, | f ₂₃₄ | /f=0.568 Example 6 f = 1, F / 7.6, IH = 0.829 2ω = 79.3 ° r ₁ ＝ ∞ d ₁ ＝ 0.1149 n ₁ ＝ 1.51633 ν _{1 = 64.15 r 2 = 0.4898 d} 2 = 0.9699 r 3 = ∞ d 3 = 0.1149 n 2 = 1.54869 ν 2 = 45.55 r 4 = ∞ d 4 = 0.1126 n 3 = 1.78590 ν 3 = 44.18 r 5 = -1.5407 d 5 ＝ 0.0689 r ₆ ＝ ∞ (aperture) d ₆ ＝ 0.2297 n ₄ ＝ 1.51633 ν ₄ ＝ 64.15 r ₇ ＝ ∞ d ₇ ＝ 0.1149 r ₈ ＝ 1.6505 d ₈ ＝ 0.2527 n ₅ ＝ 1.56384 ν ₅ ＝ 60.69 r ₉ ＝ －0.6492 d ₉ = 0.1122 r ₁₀ = -0.5428 d ₁₀ = 0.1149 n ₆ = 1.72825 v ₆ = 28.46 r ₁₁ = 9.0796 d ₁₁ = 0.1149 n ₇ = 1.72916 v ₇ = 54.68 r ₁₂ = -1.5806 d ₁₂ = 0.1654 r ₁₃ = ∞ d ₁₃ = 0.6892 n ₈ = 1.54869 ν ₈ ＝ 45.55 r ₁₄ ＝ ∞ d ₁₄ ＝ 2.0216 n ₉ = 1.68893 ν ₉ ＝ 31.08 r ₁₅ ＝ ∞ d ₁₅ ＝ 0.1263 n ₁₀ ＝ 1.51633 ν ₁₀ ＝ 64.15 r ₁₆ ＝ ∞ ｜ θ ₁ | − | θ ₂ /3|=|−18.0°｜−|3.8°/3|>0 f _B /f=1.76>1.40 | h ₁ / f ₁ | / | h ₄ / f ₄ | = 2.94> 1.15 | f ₁ | /f＝0.949, | f ₂₃₄ | / f ＝ 1.133 Example 7 f = 1, F / 7.3, IH = 0.708 2ω = 70.6 ° r ₁ ＝ ∞ d ₁ ＝ 0.0982 n ₁ ＝ 1.88300 ν ₁ ＝ 40.78 r ₂ ＝ 0.4371 d ₂ ＝ 0.0983 r ₃ ＝ ∞ d ₃ ＝ 0.0982 n ₂ ＝ 1.51633 ν ₂ ＝ 64.15 r ₄ ＝ ∞ d ₄ ＝ 0.0196 r ₅ ＝ 1.3851 d ₅ ＝ 0.1570 n ₃ ＝ 1.84666 ν ₃ ＝ 23.78 r ₆ ＝ −1.9631 d ₆ ＝ 0.0982 n ₄ ＝ 1.51633 ν ₄ ＝ 64.15 r ₇ ＝ 63.9503 d ₇ ＝ 0.4464 r ₈ ＝ ∞ (aperture) d ₈ ＝ 0.0020 r ₉ ＝ 1.6143 d ₉ ＝ 0.0982 n ₅ ＝ 1.51633 ν ₅ ＝ 64.15 r ₁₀ ＝ －0.5780 d ₁₀ ＝ 0.0981 n ₆ ＝ 1.68893 ν ₆ = 31.08 r ₁₁ = -0.7627 d ₁₁ = 0.0196 r ₁₂ = 1.5267 d ₁₂ = 0.1576 n ₇ = 1.51633 ν ₇ = 64.15 r ₁₃ = -0.7404 d ₁₃ = 0.1178 r ₁₄ = -0.5354 d ₁₄ = 0.1178 n ₈ = 1.84666 ν _{8 = 23.78 r 15 = -2.5284 d} 15 = 0.0785 r 16 = ∞ d 16 = 0.5889 n 9 = 1.51633 ν 9 = 64.15 r 17 = ∞ d 17 = 1.6686 n 10 = 1.68893 ν 10 = 31.08 r 18 = ∞ d 18 _{= 0.2945 n 11 = 1.51633 ν 11} = 64.15 r 19 = ∞ | θ 1 | - | θ 2/3 | = | -20 ° | - | 3.9 ° / 3 | _{0 f B /f=1.47>1.40 | h 1 /} f 1 | / | h 4 / f 4 | = 3.61> 1.15 | f 1 | /f=0.495 <1, | f 234 | /f=0.723 Example 8 f = 1, F / 6.8, IH = 0.714 2ω = 71.1 ° r ₁ ＝ ∞ d ₁ ＝ 0.0989 n ₁ ＝ 1.88300 ν ₁ ＝ 40.78 r ₂ ＝ 0.3189 d ₂ ＝ 0.1369 r ₃ ＝ 0.7682 d ₃ ＝ 0.0989 n ₂ ＝ 1.72825 ν ₂ = 28.46 r ₄ = 11.9171 d ₄ ＝ 0.0198 r ₅ ＝ ∞ d ₅ ＝ 0.0989 n ₂ ＝ 1.72825 ν ₃ ＝ 28.46 r ₆ ＝ －0.5935 d ₆ ＝ 0.0989 n ₄ ＝ 1.72916 ν ₄ ＝ 54.68 r ₇ ＝ ∞ _{d 7 = 0.1697 r 8 = ∞} ( _{stop) d 8 = 0.0198 r 9 =} 0.7310 d 9 = 0.1978 n 5 = 1.51633 ν 5 = 64.15 r 10 = -0.6141 d 10 = 0.0198 r 11 = 2.6598 d 11 = 0.1385 n 6 ＝ 1.51633 ν ₆ ＝ 64.15 r ₁₂ ＝ －0.6012 d ₁₂ ＝ 0.0893 r ₁₃ ＝ －0.3604 d ₁₃ ＝ 0.1187 n ₇ ＝ 1.84666 ν ₇ ＝ 23.78 r ₁₄ ＝ －1.1869 d ₁₄ ＝ 0.0791 r ₁₅ ＝ ∞ d ₁₅ ＝ 0.5935 n ₈ = 1.68893 ν ₈ ＝ 31.08 r ₁₆ ＝ ∞ d ₁₆ ＝ 1.6815 n ₉ ＝ 1.68893 ν ₉ ＝ 31.08 r ₁₇ ＝ ∞ d ₁₇ ＝ 0.2967 n ₁₀ ＝ 1.51633 ν ₁₀ ＝ 64.15 r ₁₈ ＝ ∞ ｜ θ ₁ | － ｜ θ ₂ / 3 | = | -20 ° |-| 4.2 ° / 3 |> 0 f _B /f=1.48>1.40 | h ₁ / f ₁ | / | h ₄ / f ₄ | = 2.80> 1.14 | f ₁ | / f _{= 0.361 <1, | f 234} | /f=0.541 example 9 f = 1, F / 6.6 , IH = 0.694 2ω = 69.5 ° _{r 1 = ∞ d 1 = 0.0961} n 1 = 1.88300 ν 1 = 40.78 r 2 = _{0.5274 d 2 = 0.3228 r 3 =} -19.2890 d 3 = 0.2947 n 2 = 1.88300 ν 2 = 40.78 r 4 = -68.9735 d 4 = 0.0258 r 5 = 1.2365 d 5 = 0.2500 n 3 = 1.64769 ν 3 = 33.80 r 6 = _{8.7930 d 6 = 0.3015 r 7 =} 2.3531 ( _{stop) d 7 = 0.3077 n 4 =} 1.51633 ν 4 = 64.15 r 8 = -0.9412 d 8 = 0.1154 n 5 = 1.84666 ν 6 = 23.78 r 9 = -1.1878 d 9 = 0.0192 _{r 10 = 2.7473 d 10 = 0.2966} n 6 = 1.51633 ν 6 = 64.15 r 11 = -1.1497 d 11 = 0.2049 r 12 = -0.6852 d 12 = 0.2324 n 7 = 1.88300 ν 7 = 40.78 r 13 = -1.1725 d 13 = 0.1291 r ₁₄ = ∞ d ₁₄ = 2.8846 n ₈ = 1.51633 ν ₈ = 64.15 r ₁₅ = ∞ | θ ₁ | − | θ ₂ /3|=|−13.3°｜−|4.3°/3|>0 f _B / f = 1.85> 1.40 | h ₁ / f ₁ | / | h ₄ / f ₄ | = 5.69> 1 .14 | f ₁ | /f=0.597 <1, | f ₂₃₄ | /f=1.041 Example 10 f = 1, F / 6.7, IH = 0.845 2ω = 80.4 ° r ₁ = ∞ d ₁ = 0.1173 n ₁ = 1.88300 ν ₁ ＝ 40.78 r ₂ ＝ 0.5713 d ₂ ＝ 0.4774 r ₃ ＝ 1.4113 d ₃ ＝ 0.4928 n ₂ ＝ 1.51742 ν ₂ ＝ 52.41 r ₄ ＝ －1.0827 d ₄ ＝ 0.0705 r ₅ ＝ ∞ (aperture) d ₅ ＝ 0.6102 n ₃ = 1.51633 ν ₃ = 64.15 r ₆ = ∞ d ₆ = 0.2323 r ₇ = 2.5203 d ₇ = 0.1619 6 ₄ = 1.72825 ν ₄ = 28.46 r ₈ = 0.8214 d ₈ = 0.3755 n ₅ = 1.72916 ν ₅ = 54.68 r ₉ = -0.9814 d ₉ = 0.1643 r ₁₀ = -0.7474 d ₁₀ = 0.1173 n ₆ = 1.78472 v ₆ = 25.71 r ₁₁ = -1.9794 d ₁₁ = 0.0939 r ₁₂ = ∞ d ₁₂ = 0.8214 n ₇ = 1.56138 v ₇ = 45.18 r ₁₃ ＝ ∞ d ₁₃ ＝ 0.2347 n ₈ ＝ 1.51633 ν ₈ ＝ 64.15 r ₁₄ ＝ ∞ d ₁₄ ＝ 1.2204 n ₉ ＝ 1.51633 ν ₉ ＝ 64.15 r ₁₅ ＝ ∞ ｜ θ ₁ |-｜ θ ₂ /3|=｜-9.2° ｜ − | 4.3 ° / 3 | ＞ 0 f _B /f=1.43 | h ₁ / f ₁ | / | h ₄ / f ₄ | ＝ 2.19> 1.14 | f ₁ | /f＝0.647 ＜ 1, | f ₂₃₄ | /f=1.043 Example 11 f = 1, F / 5, IH = 0.952 2ω = 87.2 ° r ₁ ＝ ∞ d ₁ ＝ 0.1846 n ₁ = 1.88300 ν ₁ ＝ 40.78 r ₂ ＝ 0.7814 d ₂ ＝ 1.1864 r ₃ ＝ 10.8176 d ₃ ＝ 0.3725 n ₂ ＝ 1.78590 ν ₂ ＝ 44.18 r ₄ ＝ 1.2548 d ₄ ＝ 0.9228 n ₃ = 1.64769 ν ₃ ＝ 33.80 r ₅ ＝ －1.6224 d ₅ ＝ 0.1318 r ₆ ＝ ∞ (aperture) d ₆ ＝ 0.2636 n ₄ ＝ 1.51633 ν ₄ ＝ 64.15 r ₇ ＝ ∞ d ₇ ＝ 0.3427 r ₈ ＝ 4.00013 d ₈ ＝ 0.3691 n ₅ = 1.53256 v ₅ = 45.91 r ₉ = -0.9441 d ₉ = 0.1318 n ₆ = 1.84666 v ₆ = 23.78 r ₁₀ = -1.5897 d ₁₀ = 0.0264 r ₁₁ = 1.8567 d ₁₁ = 0.4214 n ₇ = 1.72916 v ₇ = 54.68 r ₁₂ = -1.5819 d ₁₂ = 0.1320 n ₈ = 1.72825 ν ₈ = 28.46 r ₁₃ = 1.2837 d ₁₃ = 0.4746 r ₁₄ = ∞ d ₁₄ = 0.9228 n ₉ = 1.54869 ν ₉ = 45.55 r ₁₅ = ∞ d ₁₅ = 2.0348 n ₁₀ = 1.9680 ν ₁₀ ＝ 55.52 r ₁₆ ＝ ∞ d ₁₆ ＝ 0.0005 r ₁₇ ＝ ∞ d ₁₇ ＝ 0.2853 n ₁₁ ＝ 1.69680 ν ₁₁ ＝ 55.52 r ₁₈ ＝ ∞ d ₁₈ ＝ 0.0004 r ₁₉ ＝ ∞ d ₁₉ ＝ 0.1318 n ₁₂ ＝ 1.51633 ν ₁₂ ＝ 64.15 r ₂₀ ＝ ∞ ｜ θ ₁ | − | θ ₂ /3|＝｜−15.5°｜−|5.7°/3|>0 f _B /f=2.350>1.40 | h ₁ / f ₁ | / | h ₄ / f ₄ | = 10.9> 1.14 | f ₁ | /f=0.885 <1, | f ₂₃₄ | /f=1.582 In the data of the above example , R ₁ , r ₂ , ... are the radii of curvature of each surface of the lens, d ₁ , d ₂ , ... are the wall thickness and air gap of each lens,
n ₁ , n ₂ , ... are the refractive indices of the respective lenses, ν ₁ , ν ₂ , ... are the Abbe numbers of the respective lenses, IH is the image height, and 2ω is the angle of view.

Example 1 has a lens configuration shown in FIG. 5, in which a solid-state image sensor is obliquely arranged behind the lens system, and two prisms P ₁ and P ₂ for forming an erect image by reflecting twice in the middle and an optical system are provided. A low pass filter is installed.

In this embodiment, f _B /f=1.76, and the back focus is very long, which of course satisfies the condition.

Under these conditions, in order to make the prism part of the rear lens group compact together with the front lens, it is preferable that the chief ray of the maximum image height of the emitted light is not parallel to the optical axis but a divergent system. In order to balance the diameter of the prism with the diameter of the prism, the inclination of the chief ray in the lens system should be as small as possible. For that purpose, a strong concave surface is provided near the front of the entrance surface of the prism P ₁ , the diaphragm position is further arranged in front of it, and a negative lens group is also arranged on the entrance side on the object side, and a positive lens is arranged on the center part. The lens group was arranged. Furthermore, in order to make the rear group particularly compact, the above-mentioned conditions are satisfied.

 The aberration situation of the first embodiment is as shown in FIG.

The second to eleventh embodiments have lens configurations as shown in FIGS. 6 to 15, respectively. In these figures, all filters and prisms are shown in the form of glass blocks.

The aberration states of Examples 2 to 11 are 17th, respectively.
This is as shown in FIGS.

[Advantages of the Invention] As described above, in the objective lens of the present invention, the back focus can be made sufficiently long, an optical low-pass filter or an infrared ray removing filter can be arranged behind the objective lens, and the solid-state imaging device can be slanted. Alternatively, the tip may be placed sideways to have a smaller diameter and be compact. Also, the distortion can be made smaller than that of the retro focus type.

[Brief description of drawings]

FIG. 1 is a diagram showing the basic structure of an objective lens of the present invention, and FIG.
FIG. 3 and FIG. 3 are views showing examples of arrangement of prisms and the like in the present invention, FIG. 4 is a view showing a relationship between rear group magnification and back focus, and FIGS. 5 to 15 are Embodiments 1 to 5 of the present invention, respectively. 16 is a sectional view of Example 11, FIGS. 16 to 26 are aberration curve diagrams of Examples 1 to 11, respectively, and FIGS. 27 to 30 are diagrams showing the configuration of a conventional objective lens.

Claims (3)

(57) [Claims] 1. A solid-state image sensor, a prism disposed in front of the solid-state image sensor, and an endoscope objective lens disposed in front of the prism, wherein the solid-state image sensor has a longitudinal direction. Is obliquely inclined with respect to the axial direction of the endoscope, or is arranged in parallel to the axial direction, the endoscope objective lens is a front group having a negative refractive power in order from the object side, It has each intermediate group of positive refracting power as a whole and a final group including a concave surface in contact with air, and is arranged between the most object side surface and the most image side surface of each intermediate group, and An endoscope that satisfies the conditions of. _{(1) | θ 1 |>} | θ 2/3 | (2) | f B /f|>1.4 (3) | h 1 / f 1 |> 1.5 · | h 4 / f 4 | However, theta ₁ is The angle between the off-axis chief ray and the optical axis at the maximum angle of view, θ ₂ is the angle between the off-axis chief ray at the maximum angle of view and the off-axis ray passing through the aperture periphery, f _B is the back focus of the optical system, f ₁ is the focal length of the front group, f ₄ is the focal length of the final group, h ₁ is the average ray height at each lens surface of the front group through which the off-axis chief ray passes at the maximum angle of view, h ₄ is the maximum The average value of the ray heights at each lens surface of the final group through which the off-axis chief ray at the angle of view passes, and f is the focal length of the entire system. 2. The endoscope according to claim 1, wherein the endoscope satisfies the following conditions. (4) | f ₁ / f | <1 (5) 0.4 <| f ₂₃₄ | / f <2 where f ₂₃₄ is the focal length of the composite of the intermediate group and the final group. 3. The endoscope according to claim 2, wherein the final group has a negative lens facing the solid-state image pickup element, and the endoscope satisfies the following condition. (6) 0.2 <| R ₁ | / f <10 (7) 0.2 <| R ₄ | / f <10 where R ₁ is the radius of curvature of the concave surface of the front group and R ₄ is the radius of curvature of the concave surface of the final group. is there.